In recent years, there has been a tendency to reduce the in size of electronic devices using high frequency waves, such as digital electronic devices. And, in a digital electronic device having a high mounting density of components on a circuit board, an LSI or IC of a central processing unit (CPU), an image processor logic unit (IPLU) or the like is mounted on the circuit board. The LSI or IC is composed of a large number of semiconductor devices. Since these semiconductor devices carry out operations, such as amplification or oscillation, by receiving the supply of energy from the exterior or external source, they are generally called active elements. And, these active elements often generate inductive noise. Due to the inductive noise, high frequency magnetic fields are induced at the same surface as an element mounting surface of the circuit board and an opposite surface thereof. What is to be a problem here is a phenomenon, such as performance degradation or abnormal resonance, caused by the electrostatic coupling, an increase of the line-line coupling due to the electromagnetic coupling, or an electromagnetic interference due to radiant noise.
Conventionally, against such a so-called electromagentic interference, a measure has been taken, for example, to insert a low-pass filter into a circuit, to dispose a circuit in question at a distance or to carry out shielding, so as to suppress the electromagnetic coupling or the undesired radiant noise which causes the electromagnetic interference.
However, among the conventional measures employed to compensate for electromagnetic interference, is to insert noise filter. However, this method of carrying out the shielding is not too effective because of space requirements for mounting the noise filter. Similarly, the method of positioning the circuit in question at a distance also goes against the realization of the high density. Further, a so-called shielding method, in which a circuit subject to magnetic interference is surrounded by a metal plate or a conductive material formed by conductive plating is a technique which has been used. However, it aims to prevent leakage of the radiant noise generated in the interior to the exterior or invasion of the radiant noise from the exterior to the interior.
If the active element is too close to the semiconductive device, electromagnetic coupling is apt to occur which is undesirable. As a result, in some instances, secondary electromagnetic interference has occurred.
Therefore, an object of the present invention is to provide an EMI countermeasure component which does not adversely affects primary circuit function, but which has sufficient shielding effect against permeation of electromagnetic waves radiated to the exterior, and is further capable of suppressing a malfunction or the like due to mutual interferences between peripheral components or an electromagnetic induction to a signal line, and an active element equipped with it.